The present invention concerns a thermostatic or thermally controlled liquid mixing valve. In particular, the invention relates to a mixing valve that is suitable for use in an emergency shower or eyewash system.
Thermally controlled or thermostatic mixing valves are well known. Valves of this type receive both hot and cold liquid, typically water, and allow the liquids to mix to a predetermined temperature. The temperature is controlled by way of a thermally responsive control member, or thermostat, which maintains the liquid temperature according to the user's setting.
One particular application of thermostatic mixing valves is in connection with emergency shower and eyewash systems. Toxic and hazardous chemicals are used in many industrial environments. The Occupational Safety and Health Act of 1970 was enacted to assure that workers would be provided with safe and healthful working conditions. Pursuant to this act, the Occupational Safety and Health Administration adopted regulations which require the availability of emergency eyewash and shower equipment for use as a form of first aid treatment. Emergency shower and eyewash systems have proliferated in a wide range of industries, including automotive, food processing, chemical processing, petroleum refining steel production, pulp and paper, and waste water treatment. In each of these industries, workers are exposed to extremely hazardous chemicals which can cause serious tissue damage and destruction.
Many emergency shower and eyewash facilities are provided with ground water that is already tempered to a moderate temperature, normally in the range of 50.degree.-60.degree. F. It has been found, however, that delivered water temperatures that are too cold can have the affect of discouraging maximum effective use of the emergency equipment. For example, a worker using an emergency shower may leave the shower immediately when being deluged by a stream of 50.degree. F. water. In addition, in northern climates, the ground water itself is typically barely above freezing, usually at 35.degree. F. Under these circumstances, an emergency shower and eyewash system relying solely upon untempered ground water provides water that would be too cold to be endured even by a victim of a chemical accident.
As a result, emergency shower and eyewash systems have been modified to provide tempered water. Usually this comfortable range of temperatures is between 65.degree.-95.degree. F. In order to provide tempered water within this range, most emergency facilities include a source of very hot water, typically in the range of 140.degree.-160.degree. F., that is mixed with ambient ground water.
The thermostatic valves for emergency shower and eyewash systems must address certain problems. First, the source of water should not be interrupted when in use. The victim of a chemical accident will require continuous flow of water for a prolonged period of time. Typically, in the event of an accident, the affected area should be drenched for at least 15 minutes. Thus, the source of tempered water should be able to provide the water for at least that length of time and to maintain the temperature within a comfortable range for the accident victim. In addition, the thermostatic valve must be able to maintain the tempering of the water regardless of extreme fluctuations in the supply of hot or cold water to the thermostatic mixing valve.
Finally, the valve must be able to account for failures in the supply of hot or cold water to the valve, as well as failure of the valve itself. The valves must account for these failures without placing the user of the emergency shower or eyewash system in greater peril. For example, if the cold water supply fails and only hot water in the range of 140.degree.-160.degree. F. is provided, the user can suffer bums that may be more serious than the chemical splash that is being treated.
Thus far, no known thermostatic control valve adequately addresses all of the problems associated with providing tempered water for emergency shower and eyewash systems. While many of the systems include some provisions to account for the variety of failures that can occur, no valve is presently available that can provide virtually fail-safe performance in this arena.